The field of the invention is systems and methods for medical imaging and medical image-guided treatment. More particularly, the invention relates to systems and methods for registering pre-operative medical images of a subject to an ultrasound treatment space.
Focused ultrasound (“FUS”) is a promising technology that has shown exciting potential for treatment of brain disorders. To date, transcranial FUS has been used for non-invasive surgery for chronic pain, essential tremor, and glioblastoma. These investigations have been based on the thermal ablation of targeted brain tissue using FUS, and have been guided by magnetic resonance imaging (“MRI”), in which MRI thermometry is used to measure temperature elevations during treatment.
There are also non-thermal, cavitation-mediated applications of FUS that are being investigated pre-clinically, such as transient opening of the blood-brain barrier (“BBB”) for targeted drug delivery or sonothrombolysis for the treatment of ischemic stroke. For these interventions, MRI is useful for assessing treatment outcome, but is not well suited for real-time monitoring of cavitation processes. Additionally, MRI is not widely accessible and could be prohibitively expensive if frequent treatments are required.
Ultrasound-based monitoring and control of BBB-opening has been demonstrated in preclinical models, and it has been shown that cavitation activity can be mapped in the brain during BBB opening. These studies suggest that low-cost, ultrasound-guided treatment platforms for cavitation-mediated brain therapies may be a viable option for bringing these technologies to routine clinical practice. To practically implement such a system, however, the sound aberrations caused by geometry and heterogeneity of the skull bone must be accounted for and corrected. This is necessary not only for correcting the transmit focus, but also for eliminating image distortion when mapping cavitation activity through the skull.
The gold standard approach to implement these corrections is to use computed tomography (“CT”)-derived density and geometry information taken from pre-operative patient CT data to calculate the phase and amplitude corrections necessary to produce a sharp ultrasound focus through the skull.
In current MRI-guided treatments, the pre-operative CT images are registered with the MR-images during the treatment planning stage to bring the CT data into the ultrasound treatment space. A stereotactic frame is used to ensure that the patient's head does not move during the treatment.
Given the limitations of MRI guidance for cavitation monitoring, however, it would be desirable to provide a system and method in which pre-operative CT data can be registered to an ultrasound treatment space without the need for magnetic resonance images.